The present invention relates to a device for reflected-light photometry that determines the reflectivity of a specimen area, which is part of an objective area specifically dedicated for the determination of certain properties, especially those of the reaction area of a medical-laboratory test strip, with a light source for illuminating the specimen area, preferably with diffuse light, and a photodetector that picks up light reflected from the specimen area.
The utilization of test strips to detect medically significant components of body fluids (blood and urine) is increasing in importance. The body-fluid components that are studied result in reactions that occur on the test strips, that reveal themselves through changes in color, and that can be interpreted visually to arrive at a qualitative evaluation. The utilization of test strips and associated instruments to determine medically significant quantitative parameters is also becoming constantly more common. Very high demands with respect to precision are being made not only on the test strips but also on the instruments. The objective of the present invention is to increase the precision of the instruments.
Reflected-light photometry measures total reflectivity, which is made up of a diffuse component and an ordinary component. To determine both components together the reaction area is either illuminated directly and the diffuse reflection measured or diffusely and the direct reflection measured. The present invention relates specifically to the second type of process, and an Ulbricht globe is preferably utilized to illuminate the reaction area of a test strip with diffused light.
It is essential that the light picked up by the detector in reflected-light photometers of this design be reflected almost exclusively in practical terms from the part of the objective area that provides the properties to be detected and that will be called the specimen area herein and not be reflected from other objects that it may encounter or derive from extraneous sources. This requirement, which seems to be simple to fulfill, actually provides considerable problems when maximal precision is necessary, as in the photometry of test strips.
The instruments are subject to certain constraints that limit their performance. They must be as small and convenient as possible. Since they are often powered by batteries, the light reflected from the specimen area is often not very intense, and it is essential that it arrive as unobstructed as possible at the detector, with every possible source of interference being eliminated as completely as possible.
Since these instruments are manufactured on an industrial scale for use by laymen, especially diabetics monitoring their own sugar levels, it is also important that they be as inexpensive and simple to operate as possible, without loss of precision. Extremely narrow tolerances and time-consuming equilibration must also be avoided.